1. Technical Field
The present disclosure relates to a filtering reactor. More particularly, the present disclosure relates to a filtering reactor stage utilized in a variable-frequency driving system.
2. Description of Related Art
In the field of controlling an electrical machine or an induction motor, how to adjust the speed of the motor is an important topic. A conventional electrical machine usually utilizes a DC (Direct Current) speed modulator, and its applications are limited due to a large hardware size and a high failure rate.
The variable-frequency drive (VFD) is based on variable-frequency and active electronic-component technologies to control the output of an AC (Alternating Current) motor by adjusting the frequency and amplitude of an operation power source transmitted from an input terminal.
The variable-frequency drive is configured to change the frequency and amplitude of the AC power source supplied to the induction motor, and further to change a cycle of the kinetic magnetic field on the induction motor, such that a rotating speed of the induction motor can be adjusted smoothly. The emergence of the variable-frequency drive simplifies the speed control process, which used to be complex and difficult. The AC induction motor collaborating with the variable-frequency drive may be used to replace most of the jobs which only can be done by using the DC electrical machinery originally, such that the size of the circuitry system with the AC induction motor and the variable-frequency drive can be reduced and the failure rate can be lowered.
A conventional variable-frequency drive usually includes a rectifier and an inverter. A current ripple noise may occur on a signal transmission between the rectifier and the inverter. A common solution for filtering out the current ripple noise is to implement a capacitor on a DC bridge of one single side between the rectifier and the inverter. However, when the variable-frequency drive is in operation, two common-mode currents are generated to flow from the rectifier to the inverter via two DC bridges on both sides between the rectifier and the inverter. A conventional way to lower the common-mode currents is to implement capacitors on both DC bridges, thereby suppressing electromagnetic interference (EMI). However, the capacitors in the conventional solution may only provide limited effects on suppressing the common-mode currents.